Talking about Motomiya in Discord (since he's now in Grand Jump serializing a new manga) I want to leave a short list of the things why Shonen Jump exists thanks to Motomiya (source: many interviews like Kurumada interview, Jump L'Age d'Or book, and Shonen Jump 50th anniversaries books).
-Did the first Jump success (Otoko Ippiki Gaki Daisho. Reminder Jump reached 1 millon just thanks to Otoko Ippiki fujos)
-Convinced Akimoto that, since Kochikame hasn't "plot", he could write it like Saze-san, long and slice of life.
-In early 80s, WSM and WSS were very succesful because their romcoms (The Kabocha Wine and Urusei Yatsura), and Jump editors were thinking in transforming the magazine to an oneshots magazine or to go full romcoms too. Motomiya convinced them to serialize Hokuto no Ken (Fist of North Star) as answer to the romcom wave. And it worked.
-Kurumada became a mangaka because Motomiya. Without Motomiya, Ring ni Kakero and Saint Seiya wouldn't exist. Otokozaka (currently resurrected in Jump Plus) is a homage to Motomiya).
-Same stuff for Tetsuo Hara (artist of Hokuto no Ken). He even did a homage to Motomiya in 1995 (that was quickly axed).
-Ring ni Kakero combined Kurumada's manliness with "superpowers" (based on Astro Kyudan, which if I recall, Kurumada was an assistant) and created that new formula that Kinnikuman (Yudetamago were friends with Kurumada and fans of Motomiya), Captain Tsubasa (Takahashi was another Motomiya fan) and Hokuto no Ken were based
-Motomiya had as assistants Buronson (author of Hokuto no Ken), the other Takahashi (Ginga: Nagareboshi Gin) and Miyashita (Sakigake Otokojuku)